Photographic silver halide emulsions having high wet density retention



3,271,158 PHOTOGRAPHIC SILVER HALIDE EMULSIONS HAVING HIGH WET DENSITY RETENTION Norman Allentoff, and Louis Mt. Minsk, Rochester, N.Y.,

assignors to Eastman Kodak Company, Rochester,

N.Y., a corporation of New Jersey No Drawing. Filed Aug. 9, 1963, Ser. No. 301,177

Claims. (Cl. 96114) This invention relates to photographic silver halide emulsions and, more particularly, to gelatino-silver halide emulsions having improved wet density or covering power retention.

Various .addenda can be added to photographic silver halide emulsions to increase the covering power of the silver in the emulsion. Emulsions of increased covering power are of special interest to the emulsion maker since their use results in what is equivalent to an increase in speed at a constant silver level or to a saving in silver at a constant density level. In many applications of photographic materials such as in graphic arts processes, it is essential for the photographic technician to maintain rigid control of contrast and density in his photographic negatives or positives. In order to have time, these characteristics are often measured immediately after processing while the film is still wet. However, as pointed out by Blake and Meerkamper in The Journal of Photographic Science, vol. 9, 1961, pages 14 to 25, the wet covering power of a gelatino-silver image can change substantially during drying. With such changes of covering power on drying, the photographic technician is not able to reliably predict the ultimate contrast in density of the dried silver image by observing the film while still wet. Moreover, a loss in density on drying represents a loss of covering power, to wit, a less efiicient production of practical density for a given amount of silver. As pointed out in the noted Blake and Meerkamper publication, large grain emulsions show this effect the most. It is thus highly desirable that density or covering power changes on drying be reduced or eliminated.

It is accordingly an object of this invention to provide novel gelatino-silver halide emulsions having reduced wetdry density changes.

It is another object of this invention to provide novel gelatino-silver halide emulsions having high covering power.

It is still another object of this invention to provide novel large grain gelatino-silver halide emulsions that have improved wet density retention.

It is likewise an object of this invention to provide novel photographic gelatino-silver halide emulsions having particular utility in the graphic arts field.

It is also an object of this invention to provide new photographic gelatino-silver halide emulsions having an increased gamma for a given development time.

These and other objects of the invention are accompilshed with photographic gelatino-silver halide emulsions wherein the silver halide comprises a substantial amount of large grain silver bromoiodide, and wherein the emulsion contains a minor proportionate amount of a low molecular weight, water-soluble polyacrylamide. We have found that a narrow segment of a specific polymeric class significantly improves the wet density retention and related properties of certain large grain silver halide emulsions as outlined above and as described in more detail below.

The polyacrylamide emulsion addenda of the invention are low molecular weight, water-soluble polyacrylamides of the type described in Minsk et al., US. Patent 2,486,191

Patented Sept. 6, 1966 ice issued October 25, 1949. Such polymers have the following recurring structural unit,

0 lNHr CHgCH and have an inherent viscosity in the range of about .1 to .6, and preferably .15 to .5, as determined at 25 C. in

water. As used herein, the term inherent viscosity is determined by the formula,

2.3O log 21 C wherein m is the inherent viscosity, is the relative viscosity of water solution of the polymer divided by the viscosity of the water in the same units and at the same temperature, and C is the concentration in grams (0.25) of polymer per cc. of solution. The polyacrylamide is utilized in the present gelatino-silver halide emulsions at concentrations of about 5 percent to 50 percent, and preferably 10 to 40 percent, by weight based on the gelatin in the emulsion.

The preparation of photographic gelatino-silver halide emulsions such as are utilized with the described polyacrylamides typically involves three separate operations:

( 1) Emulsification and digestion of silver halide,

(2) The freeing of the emulsion of excess water-soluble salts, suitably by washing with water, and

(3) The second digestion or after-ripening to obtain increased emulsion speed or sensitivity, reference being made to Mees, The Theory of the Photographich Process, 1954.

The water-soluble polyacrylamides utilized in our emulsions can be added to the emulsion at any stage of the preparation of the emulsion, such as before the final digestion or after-ripening, or immediately prior to coating.

The silver halide utilized in the present photographic gelatino-silver halide emulsions comprises a substantial amount of silver bromoiodide, and preferably consists essentially of silver bromoiodide, the silver bromoiodide being .5 to 10 mole percent iodide. The silver bromoiodide crystals of suitable emulsions have a mean grain size of at least about .4 micron and more generally in the range of .4 to 1.5 microns. Other silver halides than silver bromoiodide, and silver halides having other grain sizes, can be mixed in the present gelatino-silver bromoiodide emulsions. The present emulsions are the conventional negative-type, developing-out emulsions.

The photographic gelatino-silver halide emulsions of the invention can contain conventional photographic addenda such as optical sensitizers, chemical sensitizers, antifoggants, gelatin plasticizers, gelatin hardeners, coating aids, and the like photographic addenda.

The above-described emulsions of the invention can be coated on a diversity of photographic supports in accordance with usual practice. Typical supports for the photographic emulsions of the invention include cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film, polyethylene film, polypropylene film, paper, polyethylenecoated paper, glass, and the like.

The invention is further illustrated by the following examples of preferred embodiments thereof.

EXAMPLE 1 A negative-type, developing-out, gelatino-silver bromoiodide emulsion (93% bromide, 7% iodide) wherein the silver bromoiodide had a mean grain size of 0.6 micron was prepared and coated on a polyethylene terephthalate 3,271,158 3 i film support at a coverage of 375 mg. of silver per square TABLE H foot and at a coverage of 1250 mg. of gelatin per square foot. A second identical coating was made except that Percent a water-soluble, low molecular weight polyacrylamide Am d 251 05 having an inherent viscosity of 0.30 as determined in 5 C a 7 ,352,53 water at 25 C. was incorporated into the emulsion just prior to coating at a coverage of 55 grams per mole of (1) None silver halide. Samples of the two prepared films were Folyacrylemide g molecular weigh 1.18 a. 0 then exposed 1n an Eastman 11B sensltometer, developed (3) polyacrylamide (low molecular for 5 minutes in the developer described below at about Weight) 70 F., fixed in the fixing bath described below, and thereafter Washed and dried As can be observed from the data set out in Table II Developer above, the low molecular weight polyacrylamide emulsion G. r addenda of the invention resulted in a film having sub- N-methyl-p-aminophenol sulfate 2.5 stantially less wet-dry density change than the film sample Hydroquinone 2.5 containing the high molecular weight polyacrylamide or Sodium sulfite (anhydrous) 30.0 the sample containing no polyacrylamide. Sodium metaborateoctahydrate 10.0 Example 3 Potassium bromlde 0.5 00 Water to make one m Several coatings were prepared w1th negative-type, de-

b I veloping-out, gelatino-silver halide emulsions to illustrate Fxmg all the improved results that are obtained with the large Sodium thiosulfate g 240.0 grain silver bromoiodide emulsions of the invention as Sodium sulfite (anhydrous) g 15.0 H compared to finer grain silver bromoiodide and silver Acetic acid, 2 8% cc 48.0 chlorobromide emulsions. The various coatings were Boric acid g 7.5 prepared, exposed and processed by the general method Potassium alum g 15 .0 described in Example 1. The components in the various Water to make one liter, coatings as well as the resulting percent wet-dry density Then densities of the sensitometric steps for both of the Changes are slimmanzed by the data m Table. In below. In Table III, the s1lver bromoiodlde of emulsions processed film samples were measured before and after l to 3 was 93% bromlde and 7% 1od1de, the s1lver bromodrying, the dens1ty change on drying being measured at a iodide of emulsions 4 to 6 was 96% bromide and 4% wet density of 2.0. The results are summarized by the data Set out in Table 1 below iodide, the silver bromo1od1de of emulslons 7 to 9 was 99% bromide and 1% iodide, and the silver chlorobromide of emulsions 10 to 12 was 80% chloride and 20% bromide.

TABLE III TABLE I Mean Grns. 01' Percent Grain Polyacryl- Mg. of Gel- Mg. oi Wet-Dry Percent t. Emulsion Type Size amide per atin per Ag per Density Dry Density 100 g. of sq. ft. sq. ft. Change at Addenda 7 Change at. Geltltm Density of Density of 2.0 2.0

(1) None 1.20 7.0 (1) AgBrI 0.6 None 1,000 450 7.0 (2) Polyaerylainide 1. 43 1, 0 AEBTI .6 16.0 1,000 450 None. 3) AgBrI 0.0 18.0 1,000 450 2.0

(4) AgBrI 1.0 None 1, 680 762 7.0 1. 0 1e. 0 1, 680 702 1. 5 1. 0 18.0 1, 680 762 1. 0 (7) AgBrI 0.3 None 1,000 432 None (8) AgBrI 0.3 10.0 1,000 432 4.0 The relative speed and fog of the sample containing the (9) AgBI 1,000 432 polyacrylamide were not adversely affected. As can be E102 igglgru-.. 0.2 None 381 200 11.0 11 0. 18.5 381 200 15.0 observed from the data set out in Table I, the polyacryl (12) M 23.0 381 206 1&5 amide 1mparted substanhal wet density retentlon to the gelatino-silver halide emulsion.

Exam [8 2 As can be observed from the data set out in Table III p above, substantially improved wet density retention char- Three photographic film samples were prepared and acterizes the larger grain silver bromoiodide emulsions of coated as described in Example 1 wherein one coating was the invention as is illustrated by emulsions 1 to 6 of Table the gelatino-silver bromoiodide emulsion, the second coat- III, and which wet density retention is not demonstrated ing was the gelatino-silver bromoiodide emulsion containby finer grain emulsions 7 to 12 of Table III. ing 55 grams per mole of silver halide of a water-soluble, Accordingly, the present invention provides new and low molecular weight polyacrylamide having an inherent useful photographic silver halide emulsions. viscosity of 0.30 as determined in water at 25 C., and 5 The invention has been described in detail with particuthe third coating was the gelatino-silver bromoiodide lar reference to preferred embodiments thereof, but it will emulsion containing 55 grams per mole of silver halide of be understood that variations and modifications can be efa water-soluble, high molecular weight polyacrylamide fected within the spirit and scope of the invention as dehaving an inherent viscosity of 1.68 as determined in water scribed hereinabove and as defined in the appended claims. at 25 C. The three samples were thereafter exposed in We claim: an Eastman IB sensitometer and thereafter processed as 1. A photographic gelatino-silver halide emulsion condescribed in Example 1. The wet-dry density behavior taining 5% to 50% by weight based on the said gelatin of the three coatings was thereafter observed as in Examin said emulsion of a water-soluble polyacrylamide havple 1 and summarized by the data set out in Table II ing an inherent viscosity of .1 to .6 as determined at 25 below, C. in water, said silver halide comprising a substantial described in claim 2 wherein the polyacrylamide has an inherent viscosity of about .3 as determined at 25 C. in water.

4. A photographic gelatino-silver halide emulsion as described in claim 2 wherein the silver bromoiodide has a mean grain size of about .6 microns.

5. A photographic support having coated thereon an 5 emulsion as described in claim 1.

References Cited by the Examiner FOREIGN PATENTS 861,984 3/ 1961 Great Britain.

NORMAN G. TORCHIN, Primary Examiner.

RONALD H. SMITH, Assistant Examiner. 

1. A PHOTOGRAPHIC GELATINO-SILVER HALIDE EMULSION CONTAINING 5% TO 50% BY WEIGHT BASED ON THE SAID GELATIN IN SAID EMULSION OF A WATER-SOLUBLE POLYACRYLAMIDE HAVING AN INHERENT VISCOSITY OF
 1. TO
 6. AS DETERMINED AT 25* C. IN WATER, SAID SILVER HALIDE COMPRISING A SUBSTANTIAL AMOUNT OF SILVER BROMOIODIDE HAVING .5 TO 10 MOLE PERCENT IODIDE AND A MEAN GRAIN SIZE OF AT LEAST .4 MICRON. 